How does a change in Constitution affect an NPC/monster/wild-shaped druid's hit points?

If an effect or spell changes an NPC's Constitution (e.g. the Belt of Dwarvenkind or the fortitude Ioun Stone), how does it affect that creature's max HP? I'm interested in Constitution decreases as well.

I have a player who wants to wear his dwarf belt as a collar when in wild shape, (which I could say no to) but the ioun stone seems entirely possible.

I'm also curious about how Con changes from such items/sources affect a druid in Wild Shape, if that creature can use the item.

I assume I'd modify by hit dice or CR? But that doesn't seem right.

If a wild Direwolf ((37hp(5d10+10) CR 1, CON 15 (+2)) was affected in a specific way, then should it be any different from a druid wild shaping into a Direwolf?

I was maybe thinking player level would affect this, but player level doesn't affect HP of Wild Shape. Also, if it's a level 3 druid Wild Shaped as a Direwolf, then technically that Direwolf is level 3?

I've read (here) that Wild Shaped druids (that are high enough level to maintain their form) CAN use their beasts hit dice and Con mods during short rests, leading me to believe that Con IS affected by hit dice, but it seems too easy to be correct.

Spells like polymorph and true polymorph match CR with level, but it doesn't seem like something tied to CON

This is not a duplicate question. The two questions being claimed that this duplicates are about PCs, which is a different question from NPCs like this question is asking about.

– Xanthir
Sep 7 '18 at 17:41

I have reopened this question because it is not necessarily true that the rules for PCs are the same ones to use for NPCs. This makes this not a duplicate question.

– Rubiksmoose
Sep 7 '18 at 17:43

Hi @Oak, and welcome. I'm going to throw a couple of links your way and invite you to either read more in meta.rpg.SE or hop into Role-playing Games Chat if you've got questions afterward. 1: Edit the question or answer it yourself?. 2: Can I answer my own question? (I'm curious what exactly you mean when you say "it got mad at me." If you get a moment I hope you'll let me/us know in chat.) 3. We discourage "Edit:" syntax.

– nitsua60♦
Sep 7 '18 at 23:34

2 Answers
2

If the NPC is statted up like a PC, then apply normal PC rules (gain/loss according to level). This covers wild-shaped druids too.

If it's statted up like a monster, there's no official answer; the books will always give monster HP as if it was +Con per hit die, but the hit dice are retroactively assigned to achieve this, after the designers decide about how much HP a monster should have. (In other words, a Fire Giant (CR 9) has 13 hit dice because 13d12 + 13*(+6 Con bonus) = 162 HP, which is what the designers wanted it to have. The fact that it's 13 specifically has no particular significance; it could have had more or less if they were targetting a slightly higher or lower HP.)

(Note that hit dice are not used for other level-scaling things; proficiency bonuses are assigned as if the monster's CR was its level.)

So, for a monster stat block the answer is "whatever you want". Feel free to just add/subtract based on hit dice, or just give them whatever HP you feel is appropriate. There is no "correct" answer, all stat blocks are made up tables of numbers that exist solely to give you some variety when running combats.

@Jason_c_o It wasn't when the question was first posted, hence the confusion.

– Daniel Zastoupil
Sep 7 '18 at 17:33

Yup, it wasn't clear when I posted. I've editted and removed the hedging and 3e advice.

– Xanthir
Sep 7 '18 at 17:37

What about for a druid with wild shape. That's who I'm asking for. He wants his dwarf belt as a collar (which I could say no to) but the ioun stone is entirely possible

– Oak
Sep 7 '18 at 20:17

@Oak You should edit that detail into your original question, because a wild-shaped druid PC is slightly different from "an NPC or monster" (as typically described).

– V2Blast
Sep 7 '18 at 20:57

@Xanthir, I am intrigued by your statement about hit dice being retroactively assigned. Do you have a citation for that?

– keithcurtis
Sep 7 '18 at 23:32

I would apply this formula: [New Max HP] = ([New Con Modifier] - [Old Con Modifier]) * [Number of hit dice] + [Old Max HP]

NPCs and monsters add their Constitution modifier to their total HP for each hit die, just as PCs add their Constitution modifier to their total HP for each character level.

This formula should account for the change in Constitution, whether it is increased or decreased.

Keep in mind that a significant change in Constitution could change the CR of your NPC.

I was also curious with the effects on a druids wild shape ability as well

– Oak
Sep 7 '18 at 20:12

@Oak, assuming your animal form is capable of wearing whatever magical item alters your Constitution, I would apply the same formula. Otherwise, "Equipment that merges with the form has no effect until you leave the form."

– user48255
Sep 7 '18 at 20:18

That's what I was thinking. Just trying to see if it made sense. Also thought about modding it off player level. +1 con mod on a lv 12 player is +12 hp

– Oak
Sep 7 '18 at 20:29

@Oak Please ask that question separately (about the level three druid is the dire wolf technically level three). That is a separate question. Adding additional questions to a question works against how the SE model works. Ask that as a separate question.

– KorvinStarmast
Sep 8 '18 at 1:50

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